Bisphenol A, the chemical used in plastic products that is linked to cancer and infertility, may now also reduce the effectiveness of chemotherapy treatments, a new study says.

In tests on breast cancer cells, researchers from the University of Cincinnati found that Bisphenol A (BPA) may protect cancer cells from dying off when they are exposed to anti-cancer drugs.

The findings show that this action makes "chemotherapy significantly less effective," lead study author Nira Ben-Jonathan, who has studied BPA for more than ten years, said in a statement.

The findings are published in the online edition of the journal Environmental Health Perspectives.

In recent months, research has found that:

• High levels of BPA in the blood are linked to an increased risk of developing diabetes and heart disease.
• BPA interferes with brain processes involved in learning and understanding.
• BPA causes infertility and obesity in mice.

For this most recent study, the UC researchers exposed breast cancer cells to low levels of BPA that are found in the blood of most humans.

They found that BPA acts on cancer cells in a similar manner to estrogen. Estrogen stimulates the creation of proteins that protect cancer cells from chemotherapy drugs.

Researchers have long known about this estrogen-induced effect on chemotherapy. However, they have been puzzled by the fact that some women who have less estrogen in their system, such as post-menopausal women, can still be resistant to anti-cancer medications.

The researchers said the findings will help scientists determine why these and other cancer patients, such as those with advanced stages of the disease, are resistant to chemotherapy.

"Finding out what contributes to that resistance can give us an idea of what to target in order to make chemotherapy as effective as possible," Ben-Jonathan said.

Scientists have yet to agree on how much BPA exposure, if any, is safe for humans. Humans absorb the chemical after it leaches out of products such as aluminum food cans and plastic water bottles.

A recent investigation by CTV and the Globe and Mail found that BPA leached from the lining of food cans when they were heated to temperatures similar to those used during the sterilization process.

In the wake of that research, the Canada became the first country to label BPA a dangerous substance and banned it from the manufacture of baby bottles.